[php] How to check if a row exists in MySQL? (i.e. check if an email exists in MySQL)

The following are tried, tested and proven methods to check if a row exists.

(Some of which I use myself, or have used in the past).

Edit: I made an previous error in my syntax where I used mysqli_query() twice. Please consult the revision(s).

I.e.:

if (!mysqli_query($con,$query)) which should have simply read as if (!$query).

• I apologize for overlooking that mistake.

Side note: Both '".$var."' and '$var' do the same thing. You can use either one, both are valid syntax.

Here are the two edited queries:

$query = mysqli_query($con, "SELECT * FROM emails WHERE email='".$email."'");

    if (!$query)
    {
        die('Error: ' . mysqli_error($con));
    }

if(mysqli_num_rows($query) > 0){

    echo "email already exists";

}else{

    // do something

}

and in your case:

$query = mysqli_query($dbl, "SELECT * FROM `tblUser` WHERE email='".$email."'");

    if (!$query)
    {
        die('Error: ' . mysqli_error($dbl));
    }

if(mysqli_num_rows($query) > 0){

    echo "email already exists";

}else{

    // do something

}

You can also use mysqli_ with a prepared statement method:

$query = "SELECT `email` FROM `tblUser` WHERE email=?";

if ($stmt = $dbl->prepare($query)){

        $stmt->bind_param("s", $email);

        if($stmt->execute()){
            $stmt->store_result();

            $email_check= "";         
            $stmt->bind_result($email_check);
            $stmt->fetch();

            if ($stmt->num_rows == 1){

            echo "That Email already exists.";
            exit;

            }
        }
    }

Or a PDO method with a prepared statement:

<?php
$email = $_POST['email'];

$mysql_hostname = 'xxx';
$mysql_username = 'xxx';
$mysql_password = 'xxx';
$mysql_dbname = 'xxx';

try {
$conn= new PDO("mysql:host=$mysql_hostname;dbname=$mysql_dbname", $mysql_username, $mysql_password); 
     $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
} catch (PDOException $e) {
     exit( $e->getMessage() );
}

// assuming a named submit button
if(isset($_POST['submit']))
    {

        try {
            $stmt = $conn->prepare('SELECT `email` FROM `tblUser` WHERE email = ?');
            $stmt->bindParam(1, $_POST['email']); 
            $stmt->execute();
            while($row = $stmt->fetch(PDO::FETCH_ASSOC)) {

            }
        }
        catch(PDOException $e) {
            echo 'ERROR: ' . $e->getMessage();
        }

    if($stmt->rowCount() > 0){
        echo "The record exists!";
    } else {
        echo "The record is non-existant.";
    }


    }
?>

• Prepared statements are best to be used to help protect against an SQL injection.

N.B.:

When dealing with forms and POST arrays as used/outlined above, make sure that the POST arrays contain values, that a POST method is used for the form and matching named attributes for the inputs.

• FYI: Forms default to a GET method if not explicity instructed.

Note: <input type = "text" name = "var"> - $_POST['var'] match. $_POST['Var'] no match.

• POST arrays are case-sensitive.

Consult:

• http://php.net/manual/en/tutorial.forms.php

Error checking references:

• http://php.net/manual/en/function.error-reporting.php
• http://php.net/manual/en/mysqli.error.php
• http://php.net/manual/en/pdo.error-handling.php

Please note that MySQL APIs do not intermix, in case you may be visiting this Q&A and you're using mysql_ to connect with (and querying with).

• You must use the same one from connecting to querying.

Consult the following about this:

• Can I mix MySQL APIs in PHP?

If you are using the mysql_ API and have no choice to work with it, then consult the following Q&A on Stack:

• MySql php: check if Row exists

The mysql_* functions are deprecated and will be removed from future PHP releases.

• It's time to step into the 21st century.

You can also add a UNIQUE constraint to (a) row(s).

References:

• http://dev.mysql.com/doc/refman/5.7/en/constraint-primary-key.html
• http://dev.mysql.com/doc/refman/5.7/en/alter-table.html
• How to check if a value already exists to avoid duplicates?
• How add unique key to existing table (with non uniques rows)